BOTH SIDES in the rail dispute were under pressure to restart negotiations yesterday as the network was hit by the sixth 24-hour strike by signal workers.

The conciliation service Acas is expected to approach management and union informally in the next few days in an attempt to avert a 48-hour stoppage from noon next Tuesday which is likely to disrupt services for almost three full days.

Yesterday managers and supervisors again staffed signal boxes and British Rail operated about 25 per cent of normal services. Management rejected claims by the RMT transport union that only 10 per cent of British Rail's usual number of passengers travelled by train.

There is some doubt that British Rail will be able to provide a quarter of the timetable during the two days of action next week.

Jimmy Knapp, leader of the RMT, claimed yesterday that safety was again jeopardised as allegedly unqualified managers were 'dragooned' into signal boxes instead of striking workers.

In one incident a substitute signal operator sent a passenger train into New Street station, Birmingham, after it had been closed because of a fire alert. Railtrack said the signal box controller was aware the incident was a false alarm when he allowed the 8.54am train from London Euston to run in.

At Glasgow a train for Kilmarnock was wrongly routed and the union said that the driver was so distressed that he booked off duty. Railtrack admitted the train had been misdirected, but said the man completed his shift. Four supervisors were told to work 'or else', the RMT said.

The union claimed more workers were on strike than at the start of the dispute because about 200 signalling staff had joined the union over the past month.

Railtrack last night detected a softening of Mr Knapp's approach towards the dispute when he said that he was prepared to negotiate over a lump sum and basic rates. Hitherto Mr Knapp has insisted on an 'upfront' payment for productivity improvements already achieved.

The union has rejected a package which would give signal workers a lump sum of pounds 250 for giving up their right to be paid in cash and between 16 and 26 per cent on basic rates in return for accepting a restructuring package. Union officials however said the RMT was still seeking an interim payment.

Managers operated 3,800 services yesterday with many running for the first time, including London King's Cross to Peterborough in Cambridgeshire; Gillingham, Kent, to London Victoria; and Basingstoke, Hampshire, to London Waterloo.